This invention relates to a method of manufacturing a magnetic recording film and, more particularly, to a method of manufacturing a magnetic recording film of a thin metallic film type.
Magnetic tapes of a thin metallic film type have recently been attracting attention as a high density recording medium. Such tapes are manufactured by forming a magnetic layer, as a thin metallic film, on a base film (e.g., a polyester film) by such means as vacuum evaporation, electron beam evaporation, spattering and ion plating. Their magnetic layer can be made very thin, as compared to the magnetic layer of the prior art magnetic tape of a coating type. Thus, their high frequency characteristics of recording and reproduction can be improved and their recording time can be extended, as well. For these reasons, they are well suited to high density recording.
However, in the magnetic tape of a thin metallic film type for extended recording periods, the base film should be very thin. Therefore, when vapor depositing a magnetic material such as a Co-Ni alloy on the base film, the film is subjected to thermal damage resulting in the formation of wrinkles, due to heat radiated from the vapor deposition material source; and, also, due to latent heat possessed by the evaporated metal atoms. In addition, during the process of re-crystallization of the deposited metal atoms, to form a thin film, stress is produced in the base film, due to shrinkage of the thin film. This stress causes the base film to be concavely curled on the magnetic layer side. If a magnetic tape having large wrinkles is used, drop-outs will result. Further, if a curled magnetic tape is driven, vertical movements will occur in the width direction thereof, thus deteriorating the head touch of the tape and resulting in defective tape winding.
To overcome the drawbacks described above, the applicant of the present application had earlier proposed a technique of removing curls and wrinkles by heating the film, after the evaporation process, to a temperature above the temperature of the occurrence of thermal shrinkage, while providing a predetermined tension in the film (as disclosed in Japanese Patent Application No. 56-51547). By this technique, the curls and wrinkles could be removed satisfactorily. However, fluctuations of the magnetic tape output could not be suppressed sufficiently.